The primary is unusually early this year in Maryland. The date was moved up from September to comply with federal rules requiring states to send members of the military and other Americans overseas ballots not later than 45 before a federal election.

In past elections, many of the voters who appear at early voting centers on the first day of early voting, have said they vote early because they are traveling on election day, or are volunteering for candidates and working at other polling places on election day.

That was the case at the Randallstown Community Center, where more than 100 people were in line when the polling place opened at 10 a.m. Thursday.

Still other early voting centers saw fewer people than in past elections.

At the Baltimore City Public Safety Training Center, the former Pimlico Junior High School, about 150 people had voted by 11:30 a.m.

The election judge said that was a smaller number than in primaries in both 2010 and 2012.

Statewide, the Maryland State Board of Elections told WBAL-TV around 20,000 people cast ballots on Thursday, that's the highest number for a first day of early voting for a primary election since 2010, when early voting began.

According to the Maryland State Board of Elections, ahead of the 2010 Primary Election, 77,288 voters cast their ballots early, representing 2.4% of registered voters.

Ahead of the 2010 General Election, 219,601 voters cast their ballots early, representing about 6.3% of all registered voters.